1. Field of the Invention
The present invention relates to a pre-emphasis automatic adjusting system, a method for adjusting pre-emphasis and an emphasis setting signal generating circuit and more particularly to the pre-emphasis automatic adjusting system, the method for adjusting the pre-emphasis, and the emphasis setting signal generating circuit effective for placing the best suitable pre-emphasis on a transmitting signal even when a mismatched portion occurs in a signal transmission path.
2. Description of the Related Art
Conventionally, a signal transmitting system employs its pre-emphasis automatic adjusting means. The pre-emphasis automatic adjusting means is configured to ensure normal receiving of a signal by a signal receiving circuit by removing an influence by attenuation in a signal transmission path on the signal to be transmitted from a transmitting circuit of the signal transmitting system through the signal transmission path to a receiving circuit. FIG. 7 is an example of its configurations.
In the pre-emphasis automatic adjusting system (hereafter simply referred to as a known system) shown in FIG. 7, at a time of pre-emphasis automatic adjustment, a randomly patterned signal generated in a random pattern producing section 101 is transmitted through a selector 103, transmitting circuit 105, and signal transmission path 107 to a receiving circuit 109. In the receiving circuit 109 to receive the randomly patterned signal, its Veye judging section 111 compares a voltage of the randomly patterned signal with a reference voltage from a reference potential generating section 113 to obtain a value (Veye) of an eye opening in a voltage direction. The Veye is obtained by using a sampling clock outputted from a sampling clock control section 115 which controls timing of the sampling clock showing the Veye in a central portion of the received eye opening.
When the Veye obtained as above is less than a desired Veye, a judgment result is transferred from an adjustment control section 117 to an automatic adjustment controlling section 119. The automatic adjustment controlling section 119 transmits a pre-emphasis strength adjusting signal to the transmitting circuit 105. The transmitting circuit 105 changes pre-emphasis to be placed on a transmitting signal by a specified value. Feedback control is exerted repeatedly until the above Veye becomes the maximum. The signal receiving state in which its eye opening was as shown in FIG. 8 at an initial stage of the pre-emphasis automatic adjustment described above becomes a state in which the pre-emphasis adjustment becomes the best suitable. That is, when the pre-emphasis is completed, the state of the eye opening becomes the state shown in FIG. 9.
Moreover, an example of a pre-emphasis automatic adjusting system is disclosed in Patent Reference 1 (Japanese Patent Application Laid-open No. 2004-112059). The Patent Reference 1 discloses the pre-emphasis automatic adjusting means in which a test signal transmitted from a transmitting circuit is made to be reflected by a receiving circuit and the reflected signal is effectively utilized by the transmitting circuit to achieve pre-emphasis automatic adjustment being a desired object of the invention. The disclosed pre-emphasis adjusting means is so configured that, at a time of the pre-emphasis automatic adjustment, by control from a transmitting side, a receiving terminal of a receiving circuit is opened and that, in this state, a test signal being a step pulse is transmitted from a transmitting circuit through a signal transmission path to the receiving circuit and the test signal is reflected by the receiving circuit and is returned back to the transmitting circuit.
A potential of the reflected signal is compared with a pre-set comparison potential by a comparison circuit to measure a potential difference. A controller receiving this information about the potential difference judges a magnitude of the attenuation of a high-frequency signal. If the potential of the reflected signal is larger than that of the pre-set comparison potential, the controller sends a control signal to a circuit for output strength adjustment to emphasize a high-frequency component of the transmitted signal according to the magnitude of the attenuation of the high-frequency signal.
However, the above known related system has a problem. That is, in the known system, it is necessary that circuits required for the pre-emphasis automatic adjustment are installed in both the transmitting circuit and the receiving circuit, causing an increase in circuit areas necessary to configure the transmitting circuit and the receiving circuit. In addition to the disadvantage of physical configurations, another disadvantage exists. That is, in the known system, after eye opening of the randomly patterned signal received by the receiving circuit is made calm, the Veye is measured and a pre-emphasis strength adjusting signal (emphasis strength indicating signal) is transmitted to the transmitting side. Then, emphasis corresponding to a pre-emphasis strength adjusting signal is placed on a randomly patterned signal which is transmitted to the receiving circuit and appropriateness of the emphasis placed based on the measurement of the Veye of the randomly patterned signal is judged and these procedures have to be repeated to perform the best suitable pre-emphasis automatic adjustment. This is an unavoidable technological disadvantage. This causes not only an increase in time required before the completion of adjustment but also complication of adjusting procedures.
Moreover, the pre-emphasis automatic adjusting means disclosed in the above Patent Reference 1 can resolve almost all the disadvantages of the above known system, however, the related system is configured on a presumption that an ideal signal transmission path 107b having no through hole is formed on a circuit board 107a (see FIG. 10) and a step signal is totally reflected (see FIG. 11) and, therefore, the related pre-emphasis automatic adjusting means requires further improvement.